System for combined imaging and scatterometry metrology

ABSTRACT

Metrology targets, design files, and design and production methods thereof are provided. The targets comprise two or more parallel periodic structures at respective layers, wherein a predetermined offset is introduced between the periodic structures, for example, opposite offsets at different parts of a target. Quality metrics are designed to estimate the unintentional overlay from measurements of a same metrology parameter by two or more alternative measurement algorithms. Target parameters are configured to enable both imaging and scatterometry measurements and enhance the metrology measurements by the use of both methods on the same targets. Imaging and scatterometry target parts may share elements or have common element dimensions. Imaging and scatterometry target parts may be combined into a single target area or may be integrated into a hybrid target using a specified geometric arrangement.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 14/621,026, filed on Feb. 12, 2015, which was filedunder 35 U.S.C. § 120 and § 365(c) as a continuation of InternationalPatent Application Serial No. PCT/US14/40030, filed on May 29, 2014,which application claims the benefit under 35 U.S.C. 119(e) of U.S.Provisional Patent Application No. 61/829,139, filed on May 30, 2013,U.S. Provisional Patent Application No. 61/830,729, filed on Jun. 4,2013, and U.S. Provisional Patent Application No. 61/977,075, filed onApr. 8, 2014, whereby all above-listed patent applications areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of metrology targets, andmore particularly, to metrology targets for combined imaging andscatterometry measurements.

BACKGROUND OF THE INVENTION

Metrology targets are designed to enable the measurement of parametersthat indicate the quality of wafer production steps and quantify thecorrespondence between design and implementation of structures on thewafer. Imaging metrology targets as specific structures optimize therequirements for device similarity and for optical image measurabilityand their images provide measurement data. Scatterometry metrologytargets on the other hand, yield diffraction patterns at the pupilplane, from which target parameters may be derived.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention provides a metrology targetcomprising at least two parallel periodic structures at respectivelayers, wherein a predetermined offset is introduced between theperiodic structures.

These, additional, and/or other aspects and/or advantages of the presentinvention are set forth in the detailed description which follows;possibly inferable from the detailed description; and/or learnable bypractice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of embodiments of the invention and to showhow the same may be carried into effect, reference will now be made,purely by way of example, to the accompanying drawings in which likenumerals designate corresponding elements or sections throughout. In theaccompanying drawings:

FIG. 1 is a high level schematic illustration of metrology targets,according to some embodiments of the invention;

FIG. 2A is a schematic illustration of the efficiency of the proposedtargets and measurement methods, according to some embodiments of theinvention;

FIG. 2B is a schematic illustration of the efficiency of the proposedtargets and measurement methods, according to some embodiments of theinvention;

FIG. 3 is a high level schematic illustration of metrology targets,according to some embodiments of the invention;

FIG. 4 is a high level schematic illustration of metrology targets,according to some embodiments of the invention;

FIG. 5A is a high level schematic illustration of metrology targets andregion of interest (ROI) selection, according to some embodiments of theinvention;

FIG. 5B is a high level schematic illustration of metrology targets andregion of interest (ROI) selection, according to some embodiments of theinvention;

FIG. 6 is a high level schematic illustration of a metrology target,according to some embodiments of the invention;

FIG. 7 is a high level schematic illustration of metrology targetshaving imaging and scatterometry parts, according to some embodiments ofthe invention;

FIG. 8 is a high level schematic illustration of metrology targetshaving imaging and scatterometry parts, according to some embodiments ofthe invention;

FIG. 9 is a high level schematic illustration of a segmented metrologytarget layer, according to some embodiments of the invention;

FIG. 10A is a high level schematic illustration of metrology targets,according to some embodiments of the invention;

FIG. 10B is a high level schematic illustration of metrology targets,according to some embodiments of the invention;

FIG. 10C is a high level schematic illustration of metrology targets,according to some embodiments of the invention;

FIG. 11 is a high level schematic illustration of a multi-layeredmetrology target, according to some embodiments of the invention; and,

FIG. 12 is a high level flowchart illustrating a method, according tosome embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Prior to the detailed description being set forth, it may be helpful toset forth definitions of certain terms that will be used hereinafter.

The terms “metrology target” or “target” as used herein in thisapplication, are defined as structures designed or produced on a waferwhich is used for metrological purposes. The term “layer” as used hereinin this application, is defined as any of the layers used in aphotolithography process in any of its steps. The term “layer” as usedherein in this application, may comprise different patterns on the samephysical layer, which are created in different processes or lithographysteps.

The term “periodic structure” as used in this application refers to anykind of designed or produced structure in at least one layer whichexhibits some periodicity. Periodic structures at different layers maybe configured to yield target elements which are not periodic within themeasurement resolution, e.g., when structure elements are not resolvedunder specific measurement conditions. The periodicity of periodicstructures is characterized by its pitch, namely its spatial frequency.For example, a bar as a target element may be produced as a group ofspaced parallel lines, thereby reducing the minimal feature size of theelement and avoiding monotonous regions in the target. Each element of aperiodic structure is referred to as a target element.

The term “target element” as used herein in this application, is definedas a feature in the metrology target such as individual target areas orboxes, grating bars etc. Target elements may be full or empty (gaps),and may also be segmented, i.e., may comprise multiple smaller featureswhich cumulatively constitute the target element. A target and/or aperiodic structure is referred to as comprising target elements, each“target element” being a feature of the target that is to bedistinguished from its background, the “background” being a wafer areaproximate to a target element on the same or on a different layer (aboveor below the target element). The term “crosstalk” as used herein inthis application, is defined as optical interaction between signals fromdifferent target elements, such as optical interaction between parallelperiodic structures at different layers.

The term “offset” as used herein in this application, is defined as ashift between target elements at different layers, which is intended andpredetermined. The term “overlay” as used herein in this application, isdefined as a shift between layers which includes an unintentionalcomponent (e.g., due to process inaccuracies) that may cause productioninaccuracies and is thus aim of a metrology measurement. The measured orsimulated overlay (OVL) may comprise donations from a predeterminedoffset component and from an unintentional overlay inaccuracy.

The terms “quality merit”, “quality metric”, “quality measure” and“Qmerit” are used herein throughout this application to refer to amathematical transformation of measurement results into one or morefigures of merit which may serve as metrics to characterize metrologyparameters (e.g., overlay measurements).

With specific reference now to the drawings in detail, it is stressedthat the particulars shown are by way of example and for purposes ofillustrative discussion of the preferred embodiments of the presentinvention only, and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention, the description taken with the drawings making apparent tothose skilled in the art how the several forms of the invention may beembodied in practice.

Before at least one embodiment of the invention is explained in detail,it is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangement of thecomponents set forth in the following description or illustrated in thedrawings. The invention is applicable to other embodiments or of beingpracticed or carried out in various ways. Also, it is to be understoodthat the phraseology and terminology employed herein is for the purposeof description and should not be regarded as limiting.

Metrology targets, design files, and design and production methodsthereof are provided. The targets comprise two or more parallel periodicstructures at respective layers, wherein a predetermined offset isintroduced between the periodic structures. Target parameters areconfigured to enable both imaging and scatterometry measurements andenhance the metrology measurements by the use of both methods on thesame targets. Imaging and scatterometry target parts may share elementsor have common element dimensions. Imaging and scatterometry targetparts may be combined into a single target area or may be integratedinto a hybrid target using a specified geometric arrangement.

FIGS. 1 and 3 are high level schematic illustrations of metrologytargets 100, according to some embodiments of the invention. The leftside of FIG. 1 schematically illustrates a top view of target 100,having four cells (quarters of target 100 in the non-limitingillustration), two cells 100X configured to enable metrologymeasurements in one direction (arbitrarily designated by X) and twocells 100Y configured to enable metrology measurements in anotherdirection (arbitrarily designated by Y), in the non-limiting example—Ybeing perpendicular to X. The right side of FIG. 1 schematicallyillustrates cross sectional side views of two segments of cells 100Xtarget 100. Target 100 is illustrated, in a non-limiting manner, ashaving two layers, a bottom previous layer with periodic structure 110and a top current layer with periodic structure 120. These layers mayrepresent any number of target layers and may be interspaced by anynumber of intermediate layers 90 (shown schematically in FIG. 3).Periodic structures 110, 120 may have identical pitches at regions inwhich they are parallel. The pitches may differ between measurementdirections and/or between target cells. For example, periodic structures110, 120 may have a first pitch p₁ in cells 100X and a second pitch p₂in cells 100Y. Pitches p₁, p₂ may be for example selected in the range0.5-1.5 μm. The pitches may be determined according to metrology andprocess compatibility requirements. Specific hardware of the metrologytool (e.g., short illumination wavelength, bigger effective objective NA(numerical aperture), polarized illumination and\or collection light)may be used to measure targets with smaller pitches. Predeterminedoffsets f₀ may be about 5-30 nm for substantially overlapping periodicstructures. Periodic structures 110, 120 may be shifted by half pitch,quarter pitch, or any other fraction of the pitch with respect to eachother (center of top lay bar above center of bottom layer space), and insuch cases offset ±f₀ may be defined as shifts with respect to theshifted structures.

Different offsets may be introduced in different parts of target 100,for example opposite offsets may be set at different, optionallycorresponding or paired parts of target 100 such as periodic structuresmeasured in the same measurement direction. In certain embodiments, theopposite predetermined offsets add differently to unintentional overlaysand thus allow extracting the unintentional overlays. Using imagingmetrology techniques as a non-limiting example, the unintentionaloverlay may be estimated using differences in overlay measurements bydifferent algorithms. A metrology parameter may be measured usingdifferent algorithms (e.g., imaging overlay measurements may be obtainedusing different algorithms) and the target asymmetry may be estimatedusing the difference in measurement results obtained by the differentalgorithms, for example, by processing a difference between results of asame metrology parameter by the alternative algorithms or generally byapplying a quality measure to the difference between the algorithms toestimate the target asymmetry and derive the unintentional offsettherefrom. Respective target designs and measurement algorithms are thusdisclosed herein. In certain embodiments, the difference between theresults by different algorithms may be proportional to the unintentionaloffset, as measurements for target parts with opposite predeterminedoffsets may be subtracted from each other to express the difference onlyin terms of the unintentional offset.

While FIGS. 1 and 3 represent target designs which are typicallymeasured by scatterometry techniques, these designs may be modified tobe measurable by imaging techniques.

In certain embodiments, one of periodic structures 110, 120 may be notperiodic (see e.g., target elements 130A, 130B in FIG. 11 below) or besegmented with pitch as small as the process allows (e.g., minimaldevice pitch). In the latter case, target elements in different layersmay have different segmentation pitches. The predetermined offset may bedefined by the offsets between edges of the respective elements or byedges of the respective layers, as is explained below in more detailswith respect to the unresolved measurements.

In certain embodiments, parameters of periodic structures 110, 120 maybe selected to optimize measurement conditions for both imaging andscatterometry methods. For example, periodic structures 110, 120 may belarger than customary for scatterometry measurements, but still achievesufficient measurement precision. In a non-limiting example, periodicstructure pitch may be larger than 1200 nm to enable both resolution andsufficient measurement data collection. In another example, features ofperiodic structures 110, 120 may be unresolved (e.g., have pitches muchsmaller than half the illumination wavelength) for imaging measurementsin one measurement direction but still provide enough useful informationto enhance the corresponding scatterometry measurements (see e.g., FIG.3 below). In certain embodiments, imaging and/or scatterometrymeasurements may be carried out in polarized light to enhancemeasurement resolution with respect to any relevant targets 100. Incertain embodiments, metrology measurements of targets 100 may becarried out while attenuating or blocking a zero order reflection for atleast some of the measurements, to enhance overlay detection usingimaging or scatterometry.

Metrology target 100 comprises at least two parallel periodic structures110, 120 at respective layers. A predetermined offset f₀ is introducedbetween periodic structures 110, 120, and target 100 is hence made to beat least partially asymmetric. Target parameters may be configured toenable both imaging and scatterometry measurements.

Parallel periodic structures 110, 120 may be arranged in pairs of targetcells, and the predetermined offsets that are introduced between theperiodic structures may be opposite in direction in the cells of the atleast one pair. In the non-limiting illustration of FIG. 1, oppositepredetermined offsets f₀ are introduced in the two cells in eachdirection (+f₀(1) and −f₀(1) in cells 100X as illustrated in the crosssections; +f₀(2) and −f₀(2) in cells 100Y). Predetermined offsets f₀ mayvary between the measurement directions.

Target 100 may comprise any number of target layers with respectiveperiodic structures and any number of intermediate layers 90, accordingto target design and metrology considerations.

Parallel periodic structures 110, 120 may be partially or mostlyoverlapping, as illustrated e.g., in FIG. 1, or parallel periodicstructures 110, 120 may be mostly or wholly non-overlapping, asillustrated e.g., in FIG. 3. In either case, but particularly in thelatter case, any of periodic structures 110, 120 may be unresolved withrespect to imaging metrology measurements. The central part of FIG. 3schematically illustrates a top view of target 100, having four cells,two of which configured to enable scatterometry and imaging measurementsin one direction (similar to FIG. 1). The right part of FIG. 3schematically illustrates enlarged top views of the target cells, whilethe bottom part of FIG. 3 schematically illustrates a cross section ofparallel periodic structures 110, 120. Opposite predetermined offsets f₀are introduced in the two target cells. As schematically illustrated,periodic structure 110 may extend over a larger area of target 100,beyond the cells occupied by parallel periodic structure 120. It isnoted that the sizes of targets elements in periodic structures 110, 120are not limiting and merely serve illustrative purposes. In an examplefor unresolved measurements, periodic structure 110, 120 may beconfigured to represent a continuous target element (under a givenresolution), similar to target elements 130A, 130B schematicallyillustrated in FIG. 11 below. In this respect, composite elements aredenoted by 130A, 130B in FIG. 3 as well. Imaging measurements of target100 illustrated in FIG. 3 may comprise only measuring the right and leftelement edges of target elements 130A, 130B imaged as full squaretargets. In certain embodiments, pitch p₁ may be made too small toenable scatterometry overlay measurements. Another option is to useimaging technology to measure the two empty squares (target elements130A) versus the two full squares (target elements 130B) of the currentlayer. Such imaging measurements may suffice on their own and/or tocomplement the scatterometry measurements. Furthermore, differentimaging measurement algorithms may be used in two direction measurementsof the respective feature. Taking as a non-limiting example the upperright square in FIG. 3, periodic structure 120 may have a pitch thatrenders is unresolved along the x direction, but having a target elementlength that enables measurement in the y direction. Figures of meritdiscussed below may be used to measure the symmetry breaking for bothresolved and unresolved structure. In certain embodiments, targets 100may comprise at least one of periodic structures 110, 120 which isunresolved under specified measurement conditions and/or at least one ofperiodic structures 110, 120 which comprises a single target element.

The inventors suggest that under certain measurement conditions, theintroduced predetermined offset may have an effect on metrologymeasurements that is similar to the effect of a side wall angle, forexample, similar to line 124 illustrated in FIG. 1. The inventors havefound out that crosstalk between target layers, i.e., opticalinteraction between respective illumination and measured signals fromthe layers, may result in such similarity, which may then be used toalgorithmically calculate the overlay. It is noted that such apparentside wall angle effect may depend on the direction of illumination, astarget 100 is asymmetric due to the introduced predetermined offset.

Comparing line 124 in the top and bottom side views on the right side ofFIG. 1, it is noted that the angle of the each feature edge may bedesigned to be identical. The overlap between the layers may bedescribed as a change of this edge angle. This effective angle shiftshould be zero when the overlay is zero or half pitch. Upon introducinga small horizontal overlay f₀, the angle shift of the left edge shouldbe the opposite of the right edge shift. In addition, the angle shiftshould be anti-symmetric: If the overlay is −f₀, the new shift of theright edge should be the same shift of the left edge when there isoverlay +f₀. Moreover, the shift of the left edge of the bottom leftfeature should be the same as the shift of the right edge of the topright feature. Any deviation from such anti-symmetric angle shifts maybe used to calculate the unintentional component of the overlay.

The Overlay (OVL) values calculated using imaging and scatterometry maybe used as quality merit for the measurement and target or as basis forcalculating such quality merits. If the overlay values measured byimaging and scatterometry do not match, target 100 may be identified asbeing produced at low quality. In certain embodiments, weighted OVLvalues of imaging and scatterometry measurement techniques may be used,either to report one weighted OVL value per target or to derive aweighted OVL model. In certain embodiments, the OVL values of onetechnique and quality merits measured using the second technique may beused in combination. The combination of the information from bothtechniques may yield better unified quality merits and may provideadditional geometrical information regarding the printed target. Incertain embodiments, measurement results by one technology may be usedto calibrate the second technology OVL values (for example, if onetechnique is measured faster but less accurately than the other). Ingeneral, in any of the embodiments, measurement technique, processing ofthe results and used data may be selected according to requirements.

In certain embodiments, imaging overlay may be calculated usingalgorithms adapted to target features such as a side wall angle, forexample algorithms along the lines taught by U.S. Patent Publication No.2013/0035888. In particular, such or similar algorithms may be used toestimate the degree of target asymmetry introduced by the predeterminedoffsets. For example, the measure termed Qmerit (which may be, forexample, the difference between some pre-defined OVL algorithms appliedon the same image) described in U.S. Patent Publication No. 2013/0035888was found to be proportional to this angle shift. U.S. PatentPublication No. 2013/0035888, which is incorporated herein by referencein its entirety, discloses acquiring a plurality of overlay metrologymeasurement signals from a plurality of metrology targets distributedacross one or more fields of a wafer of a lot of wafers, determining aplurality of overlay estimates for each of the plurality of overlaymetrology measurement signals using a plurality of overlay algorithms,generating a plurality of overlay estimate distributions, and generatinga first plurality of quality metrics utilizing the generated pluralityof overlay estimate distributions, wherein each quality metriccorresponds with one overlay estimate distribution of the generatedplurality of overlay estimate distributions, each quality metric being afunction of a width of a corresponding generated overlay estimatedistribution, each quality metric further being a function of asymmetrypresent in an overlay metrology measurement signal from an associatedmetrology target. Furthermore, U.S. Patent Publication No. 2013/0035888discloses determining a first process signature as a function ofposition across the wafer by comparing a first set of metrology resultsacquired from the plurality of proxy targets following a lithographyprocess and prior to a first etching process of the wafer and at least asecond set of metrology results acquired from the plurality of proxytargets following the first etching process of the wafer; correlatingthe first process signature with a specific process path; measuring adevice correlation bias following the first etching process byperforming a first set of metrology measurements on the plurality ofdevice correlation targets of the wafer, the device correlation biasbeing the bias between a metrology structure and a device of the wafer;determining an additional etch signature for each additional processlayer and for each additional non-lithographic process path of the waferas a function of position across the wafer; measuring an additionaldevice correlation bias following each additional process layer and eachadditional non-lithographic process path of the wafer; and generating aprocess signature map database utilizing the determined first etchsignature and each of the additional etch signatures and the firstmeasured device correlation bias and each additional device correlationbias, for example, the comparing may comprise determining a differencebetween a first set of metrology results acquired from the plurality ofproxy targets following a lithography process and prior to a firstetching process of the wafer and at least a second set of metrologyresults acquired from the plurality of proxy targets following the firstetching process of the wafer. Any of the embodiments of the qualitymetric disclosed by U.S. Patent Publication No. 2013/0035888 may be usedin certain embodiments of the current invention, and is referred to inthe following by the term “Qmerit”. In certain embodiments of thecurrent invention, the quality metric referred to as “Qmerit” may beused to derive a measure of target asymmetry by comparing results ofdifferent algorithms applied to the same target.

The inventors have found out, that while symmetric targets (lacking thepredetermined offsets) result in essentially similar measurements bydifferent measurement algorithms (i.e., different algorithms yield thesame results with differing levels of precision), the disclosedasymmetric targets yield differences in measurement results by differentalgorithms, because the asymmetry affects different algorithms indifferent ways. Certain embodiments of the current invention utilizethese differences, e.g., via application of Qmerit, to extract theoverlay, and in particular the unintentional offset, from thedifferences between measurement results of the asymmetric targets bydifferent algorithms. In a non-limiting example, overlay measurements ofdisclosed asymmetric targets by different imaging algorithms (e.g.,algorithms calculating average intensities, algorithms calculatingweighted averages, edge detection algorithms, algorithms calculatingcross-correlations across the target and other image processingalgorithms) yields differences between target parts having differentasymmetries, which are used to extract the unintentional component ofthe overlay. For example, in FIG. 1, the top left and the bottom rightquarters of target 100 exhibit opposite predetermined offsets f₀, whichcombine differently with an unintentional offset to yield thedifferences between different algorithms in measuring the overlay. Incertain embodiments, metrology measurements target 100 may furthercomprise deriving information regarding process and target quality anddefects by combining overlay values and quality merits of both imagingand scatterometry measurements. Process monitoring and process controlmay be enhanced by using such derived additional information.

FIGS. 2A and 2B schematically illustrate a simulation-based efficiencyof the proposed targets and measurement methods, according to someembodiments of the invention. FIG. 2A compares the calculated overlaywith respect to the real overlay, for a range of predetermined offsetsf₀ between 10-20 nm in simulation results with illumination wavelengthof 750 nm. It is noted that larger offsets allow for a narrower range ofoverlays because in the simulation the maximal overlay was fixed. Theinventors have found out that the calculated overlays are identical tothe real overlays. Similar results were found for a range ofillumination wavelengths between 600-800 nm. FIG. 2B illustrates theanti-symmetric relation between the Qmerit measure of the offset and theactual offset, indicating that this and similar measures may beeffectively used to reliably measure overlays in targets 100. Theinventors have further found out that targets 100 produce measurementswhich are sufficiently sensitive for scatterometry purposes. Theanti-symmetric relation between the Qmerit measure and the offset f₀ maybe used to calculate the overlay using the formula:

$\begin{matrix}{{OVL} = {f_{0}\frac{{{Qmerit}\left( f_{0} \right)} + {{Qmerit}\left( {- f_{0}} \right)}}{{{Qmerit}\left( f_{0} \right)} - {{Qmerit}\left( {- f_{0}} \right)}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$with Qmerit(±f₀) being Qmerit of the cell with intended shift of ±f₀.Equation 1 is a simple way to connect the overlay with the chosen figureof merit, and merely serves as a non-limiting example for suchrelations, which may be formulated in more complex ways.

In order to estimate the OVL along the x axis of targets 100 of FIG. 3,the Qmerit values of each layer and of any feature may be used. If thetwo Qmerit values of a layer are below precision then thecrosstalk-induced overlay error can be neglected; for this layer (andmeasurement conditions) layer crosstalk should not be of concern and thestandard imaging algorithm can be used. If the crosstalk is notnegligible it can be calculated using Equation 1. In certainembodiments, target 100 may be modified to allow regular overlaycalculation using, e.g., the top right and the bottom left quarters.Another method for accurate overlay calculation is calculating the xcenter of the current top right and bottom left features in addition tothe Qmerit. This value can be compared to the x center calculated usingthe current top right and bottom left features. Assuming thatcalculations for both centers should give the same value, a calibrationfunction for the Qmerit may be found. This calibration may also beapplied on different target designs on the same layer. Similar targetdesigns and methods may be applied to calculate the crosstalk-inducedOVL error due to additional layer(s) which are not part of the alignment(for example: intra layer with dummy structures). It can also be used toestimate alignment mark errors. In certain embodiments, any of periodicstructures 110, 120 may be replaced by respective features 110, 120 andmay be single non-segmented elements, such as full squares. While notperiodic, such features 110, 120 may be used in a similar fashion asunresolved periodic structures 110, 120, for example, metrologyalgorithms may be applied to detect their centers, edges, etc.,similarly to corresponding algorithms applied to unresolved periodicstructures.

FIG. 4 is a high level schematic illustration of metrology targets 100,according to some embodiments of the invention. The left side of FIG. 4schematically illustrates a top view of target 100, having four cells(quarters of target 100 in the non-limiting illustration), two cellsconfigured to enable metrology measurements in one direction and twocells configured to enable metrology measurements in another direction,similarly to target 100 illustrated in FIG. 1. A frame 122 may be addedto target 100 to enhance positioning accuracy. The right side of FIG. 4schematically illustrates enlarged top views of the target cells. Target100 is illustrated, in a non-limiting manner, as having two layers, abottom previous layer with periodic structure 110 and a top currentlayer with periodic structure 120. These layers may represent any numberof target layers and may be interspaced by any number of intermediatelayers.

In the illustrated case parallel periodic structures 110, 120 arecompletely non-overlapping, and the relation between respectivestructure pitches and the predetermined offsets are selected to leavespecified gaps between adjacent target elements of parallel periodicstructures 110, 120. As illustrated for one measurement direction, pitchp₁ and offsets ±f₀ may be selected to leave gaps d₁, d₂ between adjacenttarget elements. The extent of overlapping between parallel periodicstructures 110, 120 may be similar or different when compared to cellsin different measurement directions. In certain embodiments, adifference in the degree of overlapping may vary between cells in thesame measurement direction. Target 100 illustrated in FIG. 4 may beunresolved for imaging purposes along at least one measurement direction(e.g., d₁, d₂ smaller than illumination wavelength), as discussed aboveregarding FIG. 3.

Parallel periodic structures 110, 120 may differ in at least one oftheir dimensions. For example, as illustrated in FIG. 3, periodicstructure 120 may have shorter target elements than periodic structure110. Clearly, the differences in dimensions may be opposite (targetelements of structure 110 being shorter than target elements ofstructure 120), or vary between measurement directions and/or cells.Other dimensions may vary in size between structures 110, 120, such asthe width of the target elements. Target elements of periodic structures110, 120 may be segmented, and segmentation characteristics (e.g.,segmentation pitch, segment dimensions) may vary between structures 110,120.

FIGS. 5A and 5B are high level schematic illustrations of metrologytargets 100 and ROI selection, according to some embodiments of theinvention. FIGS. 5A and 5B illustrate in a non-limiting manner,dimensional variation among parallel periodic structures 110, 120. Forexample, in FIG. 5A, periodic structures 120 are shorter than periodicstructures 110 (I₂(1)<I₁(1) in cells 100X and I₂(2)<I₁(2) in cells100Y), and are partially overlapping, while in FIG. 5B, periodicstructures 120 are shorter than periodic structures 110 in the Xmeasurement direction, i.e., in cells 100X, and are longer than periodicstructures 110 in the Y measurement direction, i.e., in cells 100Y(I₂(1)<I₁(1) in cells 100X and I₂(2)>I₁(2) in cells 100Y), and arepartially overlapping.

FIGS. 5A and 5B further illustrate selection of the regions of interest(ROI's 115, 125) for imaging measurements in the target designs. ROI's115, 125 may be selected with respect to dimensions of respectiveperiodic structures 110, 120 which are imaged. For example, ROI's 115,125 may be selected to include respective imaged periodic structures110, 120 and exclude target elements of periodic structures 120, 110(respectively) which are outside the area of the acquired structure. Forexample, ROI 125 at the top right quarter of target 100 illustrated inFIG. 5B encloses periodic structure 120 and its immediate surroundingsand excludes target elements of periodic structure 110 which extendbeyond the region occupied by periodic structure 120. Hence, shorteningsome of the periodic structures may enable measurements of the layerfeature edges which may be used to derive additional informationregarding the layer's center of symmetry. In some configurations itenables overlay calculation using standard algorithms (when thecrosstalk between the different layer feature edges is negligible). Thedifference between the center of symmetry as extracted from ameasurement algorithm taking into account the asymmetric structure ofthe target (e.g., Qmerit) and the center of symmetry as extracted from astandard algorithm (assuming symmetric targets) may be calculated andused to estimate using a different approach the target's asymmetry.Another possibility is to use a CD to space ratio (i.e., the ratiobetween target element widths and the widths between target elements)different than one. Any parameters of periodic structures 110, 120 andtarget 100, such as intended shifts (predetermined offsets), coarsepitches (p₁, p₂), target element dimensions (I₁, I₂), segmentation CDand pitch, and direction and other target design parameters may beoptimized to provide better results and enhance the synergy in usingboth imaging and scatterometry techniques on targets 100.

FIGS. 4 and 5A/5B implement similar design principles for differenttarget configurations, namely bar over trench and bar over bar designs,respectively. The measurement of any of the target designs as resolvedor unresolved elements depends on the selection of element dimensions,pitches and offsets, which may be carried out according to metrologyspecifications.

FIG. 6 is a high level schematic illustration of metrology target 100,according to some embodiments of the invention. In the illustrated topview, parallel periodic structures 110, 120 are largely overlapping,having relatively small predetermined offsets (±f₀(1) and ±f₀(2)).Widths w₁ and w₂ of the target elements in periodic structures 110, 120may be selected to optimize imaging and scatterometry performance.

FIGS. 7 and 8 are high level schematic illustrations of metrologytargets 100 having imaging and scatterometry parts 100I, 100Srespectively, according to some embodiments of the invention. Targets100 may be configured to have a scatterometry part 100S with the atleast two parallel periodic structures 110, 120 having the predeterminedoffset therebetween, and an imaging part 100I lacking the predeterminedoffset. FIG. 7 illustrates imaging part 100I adjacent to scatterometrypart 100S; FIG. 8 illustrates imaging part 100I enclosing scatterometrypart 100S. Target elements in scatterometry part 100S and in imagingpart 100I may share at least one dimension.

A illustrated in FIG. 7, cells 100SX, 100SY in two measurementdirections of scatterometry part 100S may comprise parallel periodicstructures 110, 120 having predetermined offsets therebetween. Cells100SX, 100SY may have similar or different pitches p₁, p₂ and offsetsf₀(1, 2). Cells 100IX, 100IY in two measurement directions of imagingpart 100I may comprise periodic structures 110I, 120I, which may beparallel or respectively continuous, and configured according to imagingrequirements. At least some dimensions of periodic structures 110I, 120Imay be similar to dimensions of periodic structures 110, 120 inscatterometry part 100S, while other dimensions may differ. For example,in the non-limiting illustrated case, pitches p₁, p₂ and target elementwidths may be similar while target element lengths may differ.

As illustrated on the left side of FIG. 8, the cells in two measurementdirections of scatterometry part 100S, which is in the illustrated caseenclosed within imaging part 100I, may comprise parallel periodicstructures 110SX, 120SX, 110SY, 120SY having predetermined offsetstherebetween. The cells may have similar or different pitches p₁ p₂ andoffsets. Cells 100IX, 100IY in two measurement directions of imagingpart 100I, configured to enclose scatterometry part 100S, may compriseperiodic structures 110IX, 120IX, 110IY, 120IY, which may be arranged toenclose scatterometry part 100S, e.g., by forming a frame around itsperiphery, and be configured according to imaging requirements. At leastsome dimensions of the target elements in imaging part 100I may besimilar to dimensions of target elements in scatterometry part 100S,while other dimensions may differ. For example, in the non-limitingillustrated case, pitches p₁, p₂ and target element widths may besimilar while target element lengths may differ.

In any of the target designs, dimensions of parallel periodic structures110, 120 may be selected to comply with requirements for both imagingand scatterometry measurements. In any of the target designs, targetelements of periodic structures 110, 120 may be segmented to comply withproduction requirements, e.g., comply with design rules, as well as withthe requirements for both imaging and scatterometry measurements. In anyof the target designs, background regions of target elements of periodicstructures 110, 120 may be segmented to comply with productionrequirements, e.g., comply with design rules, as well as with therequirements for both imaging and scatterometry measurements.

FIG. 9 is a high level schematic illustration of segmented metrologytarget layer 100, according to some embodiments of the invention. Thesegmentation may be applied to whole target 100 or to parts of target100, e.g., to scatterometry part 100S. Periodic structures 110, 120 inany part of target 100, and/or their respective background regions 111,121 in any of the target layers may be segmented in directions thatmaintain or enhance imaging and/or scatterometry measurements.Measurement algorithms and optics may be adjusted to enhance imagingand/or scatterometry results of targets 100 (e.g., use polarized light,compare imaging and scatterometry measurements etc.). Some regions oftarget 100 may be segmented while others may be left blank, e.g.,Scatterometry part 100S may be segmented while imaging part 100I may beunsegmented or vice versa. Measurement considerations regarding each ofparts 100I, 100S may be used to determine the form of segmentation,e.g., imaging contrast and diffraction pattern features, respectively.Segmented target 100 may be measured with polarized light to enhancecontrast and resolution of either or both imaging and scatterometrymeasurements. In the illustrated example, target elements 110/120 (thedouble notation relates to target elements in lower/upper(previous/current) layer respectively), may be segmented with pitchp_(x,t) in the x measurement direction and with pitch p_(y,t) in the ymeasurement direction, wherein the pitches in the different directionsmay differ. Similarly, backgrounds 111/121 (referring to backgrounds inlower/upper layer respectively) may be segmented vertically to targetelements 110/120 with respective pitches p_(x,b), p_(y,b) which may bedifferent or similar. Different patterns may be applied to segmentationof target elements 110/120 and/or backgrounds 111/121. The target designof FIG. 9 may be implemented in one or more of the layers in metrologytarget 100.

FIGS. 10A-10C are high level schematic illustrations of metrologytargets 100, according to some embodiments of the invention. FIGS.10A-10C illustrate targets 100 having parallel periodic structures 110,120 which differ in pitch p and/or element width w. FIG. 10Aschematically illustrates a top view of target 100 having periodicstructure 120 with wider elements and larger pitch than periodicstructure 110. Similarly to FIG. 3, some of the target features may beunresolved in imaging measurements yet be used to enhance respectivescatterometry measurements. FIGS. 10B and 10C schematically illustratecross sections of two configurations of parallel periodic structures110, 120, namely with pitches and element widths of p₁, w₁ and p₂, w₂,respectively. In both cases the predetermined offsets are denoted by f₀.It is noted that target 100 of FIG. 10B is designed to have partial areacoverage (in top view) by periodic structures 110, 120 while that target100 of FIG. 10C is designed to have full area coverage (in top view) byperiodic structures 110, 120, making the periodic structures in thelatter unresolved along the measurement direction using imagingmeasurements. Periodic structure 110 in FIGS. 10A, 10B may be designedto be unresolved while periodic structure 120 in may be designed to beresolved in the metrology measurements.

FIG. 11 is a high level schematic illustration of multi-layeredmetrology targets 100, according to some embodiments of the invention.FIG. 11 illustrates targets 100 having target elements 130A, 130B inadditional layers above (or below or intermediate between) parallelperiodic structures 110, 120. Overlays between one or both layers oftarget elements 130A, 130B and periodic structures 110, 120 may bemeasured using imaging techniques. Target elements 130A, 130B maycomprise periodic structures which are parallel or perpendicular ofperiodic structures 110, 120 and respective predetermined offsets may beintroduced between any pair of periodic structures. Target elements130A, 130B may be segmented. Imaging and/or scatterometry measurementsmay be used to measure any combination of the layers.

Certain embodiments of the disclosed invention comprise any of imagingmeasurements, scatterometry measurements, a combination thereof andimaging-enhanced scatterometry measurements of any of targets 100 andtheir variants. Furthermore, certain embodiments of the disclosedinvention comprise target design files of any of targets 100 and theirvariants.

In certain embodiments, in order to improve the imaging signal to noiseratio, the zero order of the reflected light may be attenuated orblocked. In addition to overlay measurements, targets 100 may bedesigned to enable measurements of other metrology parameters, such asCD-SEM (scanning electron microscopy imaging of critical dimensions)using respective measurement techniques and metrics.

The inventors have found out that combining data from imaging andscatterometry measurement techniques applied to the same targetssignificantly enhances metrology measurements, such as overlaymeasurements. While optical crosstalk between different layers is, inthe prior art, a major constraint in overlay target design, thedisclosed target designs overcome this issue, estimate the extent ofcrosstalk and utilize the crosstalk to measure the overlay moreaccurately and/or using smaller targets. In order to estimate theoverlay error that induced by layer crosstalk targets 100 are designedwith induced shifts (predetermined offsets) between the current and theprevious layer, having respective periodic structures. Furthermore, thecombination of different measurement techniques may be used to extractthe overlay and additional process information. For example, thescatterometry may provide information about layer thickness variationswhile the imaging provides information about the side wall angle. Thiscan be used to extract additional data about the target shape andprocess variations.

FIG. 12 is a high level flowchart illustrating a method 200, accordingto some embodiments of the invention. Method 200 may comprise stages fordesigning and/or producing targets 100, as well as configuringrespective target design files. Method 200 may further comprisemeasurement stages of targets 100. Method 200 may comprise any of thefollowing stages, irrespective of their order.

Method 200 may comprise designing intentionally asymmetric targets toenhance scatterometry overlay measurements (stage 205) and/orintroducing a predetermined offset between overlapping parallel periodicstructures of different target layers (stage 210). Stage 210 maycomprise introducing the offset between non-overlapping elements, suchas parallel periodic structures (stage 212) and/or introducing theoffset between overlapping elements, such as parallel periodicstructures (stage 214).

Method 200 may further comprise introducing different offsets indifferent parts of the target (stage 216), for example setting oppositeoffsets at different, optionally corresponding parts of the target(stage 218). In certain embodiments, the opposite predetermined offsetsadd differently to unintentional overlays and thus allow extracting theunintentional overlays from differences in overlay measurements bydifferent algorithms. In certain embodiments, method 200 may furthercomprise measuring targets wherein at least one of the periodicstructures is unresolved under specified measurement conditions and/orwherein at least one of the periodic structures comprises a singletarget element.

Method 200 may comprise measuring a metrology parameter using differentalgorithms (stage 230), e.g., obtaining imaging overlay measurementsusing different algorithms (stage 232); estimating the target asymmetryusing the difference in measurement results obtained by the differentalgorithms (stage 235), e.g., by processing a difference between resultsof a same metrology parameter by at least two alternative algorithms(stage 240) or generally applying a quality measure to the differencebetween the algorithms to estimate the target asymmetry and derive theunintentional offset therefrom (stage 245).

Method 200 may further comprise evaluating crosstalk between theperiodic structures with respect to the introduced offset (stage 220)and adjusting the dimensions of the target elements with respect to theevaluate cross talk (stage 225). In certain embodiments, stage 220 maycomprise measuring the overlay as side wall angle components usingspecified algorithms (stage 222). In certain embodiments, stage 220 maycomprise designing one or more periodic structures to be unresolvedelements in imaging measurements (stage 227).

Method 200 may comprise designing intentionally asymmetric targets toprovide imaging and scatterometry measurements simultaneously (stage250) and adjusting the dimensions of the target elements to optimize thesimultaneous imaging and scatterometry measurements (stage 255). Method200 may comprise combining and coordinating imaging structures andscatterometry structures into a single hybrid target (stage 260). Method200 may for example comprise designing the hybrid target to haveadjacent imaging and scatterometry parts (stage 262) or designing thehybrid target to have an imaging part enclosing a scatterometry part(stage 264). Method 200 may comprise any of the following stages: usingimaging measurements to enhance scatterometry measurements (stage 270),comparing measured quantities between the imaging and scatterometrymeasurements (stage 272) and configuring measurement conditions tooptimize the utilization of the simultaneous imaging and scatterometrymeasurements (stage 274). Comparison 272 may further comprise any of thefollowing: comparing imaging and scatterometry measurements, enhancingone of imaging and scatterometry measurements by the other, andselecting imaging and scatterometry measurements according to temporalor spatial requirements. In certain embodiments, method 200 may furthercomprise deriving information regarding process and target quality anddefects by combining overlay values and quality merits of both imagingand scatterometry measurements. Method 200 may further compriseimproving process monitoring and/or process control using the derivedinformation.

Method 200 may further comprise configuring the metrology target to havea scatterometry part with the at least two parallel periodic structureshaving the predetermined offset therebetween, and an imaging partlacking the predetermined offset. Method 200 may comprise designing atleast some of the target elements in the scatterometry part and in theimaging part to share at least one dimension. Method 200 may compriseusing similar target elements for both imaging and scatterometry parts(stage 266).

Method 200 may comprise introducing a predetermined offset between atleast two parallel periodic structures at respective layers of ametrology target, e.g., at a scatterometry part of the target only(stage 265). Method 200 may comprise selecting dimensions of the atleast two parallel periodic structures to comply with requirements forboth imaging and scatterometry measurements and configuring respectivetarget parameters to enable both imaging and scatterometry measurements.Method 200 may comprise configuring the at least two parallel periodicstructures to have at least one different dimension and selecting animaging region of interest (ROI) as an area in which the at least twoparallel periodic structures are at least partially overlapping.

Method 200 may comprise any of the following stages: segmenting at leastsome of the target elements of the periodic structures (stage 280),segmenting background regions of at least some target element of theperiodic structures and providing target elements in additional layers(stage 285).

Method 200 may further comprise producing respective target design filesand targets (stage 290), carrying out any of the designing andcalculation by a computer processor (stage 292) and carrying outmetrology measurements of the produced targets (stage 294), e.g., usingpolarized light for at least some of the measurements (stage 295).Method 200 may further comprise attenuating or blocking a zero orderreflection during at least some of the measurements, e.g., to enhanceoverlay detection using first or higher order scatterometry patterns.

Advantageously, with respect to prior art such as U.S. PatentPublication No. 2013/0208279 which discloses image based overlaymeasurements performed using an overlay target that includes shiftedoverlying gratings, the current disclosure combines imaging andscatterometry target structures, provides simultaneous or sequentialmeasurements of the target using both imaging and scatterometrytechniques, optimizes target structures with relation to therequirements of both techniques, and further discloses mutualenhancement of measurement results through the combination of themeasurement methods. As explained above, targets 100 allow flexibleselection and configuration of the specific measurement techniques andthe disclosure further provides a wide range of measurement processingembodiments which may be used to optimize the extraction of usefulinformation from the target measurements, with respect to givenrequirements. Furthermore, disclosed methods 200 enable derivingmetrology measurements from, and applying of metrology algorithms to,both resolved and unresolved target elements, structures and features.In particular, measuring unresolved features enables reducing the sizeof the smallest target elements to be close to or even reach thedimensions of device elements, thus making metrology targets morereliable in representing device features and less prone to processassociated inaccuracies resulting from their larger dimensions.

In the above description, an embodiment is an example or implementationof the invention. The various appearances of “one embodiment”, “anembodiment”, “certain embodiments” or “some embodiments” do notnecessarily all refer to the same embodiments.

Although various features of the invention may be described in thecontext of a single embodiment, the features may also be providedseparately or in any suitable combination. Conversely, although theinvention may be described herein in the context of separate embodimentsfor clarity, the invention may also be implemented in a singleembodiment.

Certain embodiments of the invention may include features from differentembodiments disclosed above, and certain embodiments may incorporateelements from other embodiments disclosed above. The disclosure ofelements of the invention in the context of a specific embodiment is notto be taken as limiting their use in the specific embodiment alone.

Furthermore, it is to be understood that the invention can be carriedout or practiced in various ways and that the invention can beimplemented in certain embodiments other than the ones outlined in thedescription above.

The invention is not limited to those diagrams or to the correspondingdescriptions. For example, flow need not move through each illustratedbox or state, or in exactly the same order as illustrated and described.

Meanings of technical and scientific terms used herein are to becommonly understood as by one of ordinary skill in the art to which theinvention belongs, unless otherwise defined.

While the invention has been described with respect to a limited numberof embodiments, these should not be construed as limitations on thescope of the invention, but rather as exemplifications of some of thepreferred embodiments. Other possible variations, modifications, andapplications are also within the scope of the invention. Accordingly,the scope of the invention should not be limited by what has thus farbeen described, but by the appended claims and their legal equivalents.

What is claimed is:
 1. A system comprising: one or more metrology tools, wherein the one or more metrology tools comprise at least one of an imaging metrology tool or a scatterometry metrology tool, wherein the one or more metrology systems are configured to measure at least one of an image or a scatterometry signal from a metrology target, wherein the metrology target comprises: a first layer and at least a second layer, wherein the at least the second layer is positioned above at least a portion of the first layer; and two or more target cells, wherein at least some of the target cells of the two or more target cells include a first set of periodic structures formed in the first layer and at least a second set of periodic structures formed in the at least the second layer, wherein adjacent periodic structures in the first set of periodic structures are separated by a first selected pitch, wherein adjacent periodic structures in the second set of periodic structures are separated by a second selected pitch, wherein the first selected pitch between adjacent periodic structures in the first set of periodic structures is equal to the second selected pitch between adjacent periodic structures in the at least the second set of periodic structures within at least some of the target cells of the two or more target cells, wherein a periodic structure in the first set of periodic structures is separated from a corresponding periodic structure in the at least the second set of periodic structures by a predetermined offset, wherein a periodic structure in the first set of periodic structures and a corresponding periodic structure in the second set of periodic structures are parallel, wherein a periodic structure in the first set of periodic structures includes at least one different dimension from a corresponding periodic structure in the at least the second set of periodic structures; and a processor configured to: receive one or more metrology measurements from the one or more metrology tools; and perform one or more analysis procedures on the received one or more metrology measurements.
 2. The system of claim 1, wherein a first target cell of the two or more target cells includes a different predetermined offset than at least a second target cell of the two or more target cells.
 3. The system of claim 1, wherein a first target cell of the two or more target cells includes an opposite predetermined offset than at least a second target cell of the two or more target cells.
 4. The system of claim 1, wherein the two or more target cells are configured with at least one of a selected pitch or a predetermined offset usable for both obtaining one or more imaging measurements and obtaining one or more scatterometry measurements.
 5. The system of claim 1, wherein the two or more target cells include a first target cell and at least a second target cell, wherein a predetermined offset between a periodic structure in a first set of periodic structures and a corresponding periodic structure in at least a second set of periodic structures in the first target cell is opposite in direction from a predetermined offset between a periodic structure in a first set of periodic structures and a corresponding periodic structure in at least a second set of periodic structures in the at least the second target cell.
 6. The system of claim 1, wherein a periodic structure in the first set of periodic structures and the corresponding periodic structure in the second set of periodic structures within at least some of the target cells of the two or more target cells are at least partially overlapping.
 7. The system of claim 1, wherein a periodic structure in the first set of periodic structures and the corresponding periodic structure in the second set of periodic structures within at least some of the target cells of the two or more target cells are non-overlapping.
 8. The system of claim 1, wherein the first selected pitch between adjacent periodic structures in the first set of periodic structures differs in at least one dimension from the second selected pitch between adjacent periodic structures in the at least the second set of periodic structures within at least some of the target cells of the two or more target cells.
 9. The system of claim 1, wherein at least one of the first set of periodic structures or the at least the second set of periodic structures within at least one target cell of the two or more target cells are unresolved under specified measurement conditions, wherein the specified measurement conditions are dependent on a pitch size of set of periodic structure relative to an illumination wavelength.
 10. The system of claim 1, wherein at least one periodic structure of the first set of periodic structures and a corresponding periodic structure of the at least the second set of periodic structures within at least some of the target cells of the two or more target cells form a single target element.
 11. The system of claim 1, wherein at least one of a selected pitch or a predetermined offset within at least some of the target cells of the two or more target cells are selected to comply with requirements for both obtaining one or more imaging measurements and obtaining one or more scatterometry measurements.
 12. The system of claim 1, wherein the metrology target comprises: a scatterometry part configured for obtaining scatterometry measurements, wherein the scatterometry part includes the two or more target cells, wherein at least some of the target cells of the two or more target cells include the first set of periodic structures formed in the first layer and at least the second set of periodic structures formed in the at least the second layer, wherein at least some of the target cells of the two or more target cells include a periodic structure of the first set of periodic structures separated from a corresponding periodic structure of at least the second set of periodic structures by a predetermined offset; and an imaging part configured for obtaining imaging measurements, wherein the imaging part includes at least a third periodic structure formed in the first layer and at least a fourth periodic structure formed in the at least the second layer, wherein the at least the third set of periodic structures and the at least the fourth set of periodic structures are proximate to the two or more target cells, wherein a periodic structure of the at least the third periodic structure and a periodic structure of the at least the fourth periodic structure not separated by a predetermined offset.
 13. The system of claim 12, wherein the imaging part is adjacent to the scatterometry part.
 14. The system of claim 12, wherein the imaging part encloses the scatterometry part.
 15. The system of claim 12, wherein target elements in the scatterometry part and in the imaging part share at least one dimension.
 16. The system of claim 1, wherein at least one target element formed by at least one periodic structure of the first set of periodic structures and a corresponding periodic structure of the at least the second set of periodic structures within at least some of the target cells of the two or more target cells are segmented.
 17. The system of claim 1, wherein at least a background region of at least one target element formed by at least one periodic structure of the first set of periodic structures and a corresponding periodic structure of the at least the second set of periodic structures within at least some of the target cells of the two or more target cells are segmented.
 18. The system of claim 1, wherein the one or more analysis procedures are carried out by a first algorithm and a second algorithm, wherein the first algorithm and the second algorithm are configured to process a difference between results of a same metrology parameter.
 19. The system of claim 1, wherein the one or more processors are further configured to perform at least one of: a comparison between imaging and scatterometry measurements; an enhancement of imaging and scatterometry measurements; and a selection of imaging and scatterometry measurements according to one or more temporal or spatial requirements.
 20. The system of claim 1, wherein the one or more processors are further configured to: derive information regarding process and target quality and defects by combining overlay values and quality merits of both imaging and scatterometry measurements.
 21. The system of claim 1, wherein the one or more metrology tools are configured to utilize polarized light for at least some of the measurements.
 22. The system of claim 1, wherein the one or more metrology tools are configured to at least one of attenuate or block a zero order reflection for at least some of the measurements. 